1. Field of the Invention
The present invention relates to a monolithic ceramic electronic component such as a laminated capacitor, and a method for manufacturing the same. In more detail, the present invention relates to a monolithic ceramic electronic component having a structure in which the adhesion between internal electrode and ceramic has been improved, and a method for manufacturing the same.
2. Description of the Related Art
Monolithic ceramic electronic components comprise a structure in which one or more internal electrodes are disposed within a sintered ceramic body. Monolithic ceramic electronic components known in the art include a laminated capacitor and laminated ceramic multilayer substrate.
A sintered ceramic body in which ceramic layers are laminated via internal electrodes is used for a monolithic ceramic electronic component. Adhesion between the internal electrode and the ceramic layer is aggressively required to be high in this sintered ceramic body. When the adhesive property between the ceramic layer and internal electrode is insufficient, an interlayer peeling phenomenon called delamination occurs, or a plating liquid invades the ceramic sintered body while forming external electrodes, sometimes resulting in peeling between the internal electrode and ceramic.
Occurrence of delamination as described above causes a decrease of insulation resistance, or deterioration of electrical characteristics required for use as electronic components such as capacitors.
Accordingly, various methods for improving the adhesive property has been attempted including forming perforation holes through the internal electrode to enhance the adhesive property between the ceramic layers at the upper and lower parts of the internal electrode, or mixing the same ceramic material as used in the ceramic sintered body into an electrode paste for forming the internal electrode to allow the ceramic in the internal electrode to diffuse toward the ceramic sintered body during firing.
However, the shape of the internal electrode turns out to be complicated in the ceramic electronic components manufactured by forming the perforation holes through the internal electrode, thus failing to obtain sufficient electrical characteristics.
Although the adhesive property between the internal electrode and ceramic is enhanced to some extent when the ceramic has been mixed with the internal electrode paste to allow the ceramic to diffuse toward the ceramic sintered body during firing, the adhesion between the internal electrode and the ceramic has been not always sufficient.
Accordingly, the object of the present invention is to provide a method for manufacturing a highly reliable monolithic ceramic electronic component in which the adhesive property between the internal electrode and the ceramic is effectively enhanced to decrease the occurrence of the interlayer peeling phenomenon such as delamination, and a method for manufacturing the same.
In accordance with the first aspect, the present invention provides a method for manufacturing a monolithic ceramic electronic component comprising the steps of: preparing a non-fired ceramic green chip comprising at least one layer of an internal electrode while containing a metallic compound that forms a compound by forming a solid solution with or by reacting with the internal electrode during firing; firing the green chip to allow the metal constituting the metallic compound to form a solid solution with the internal electrode or to react with the internal electrode to form a compound; and forming external electrodes on the outer surfaces of the sintered body.
In a second aspect, the present invention also provides a method for manufacturing a monolithic ceramic electronic component comprising the steps of: preparing a non-fired ceramic green chip comprising at least one layer of internal electrodes while containing a metallic compound that segregates on an internal electrode or at the periphery the internal electrode during firing the internal electrodes; obtaining a ceramic sintered body by firing the ceramic green chip while allowing the metallic compound to segregate on an internal electrode or at the periphery of the internal electrode; and forming external electrodes on the outer surfaces of the sintered body.
In the present invention according to the first and second aspects, the metallic compound containing a metal that forms a solid solution with the internal electrode or reacts with the internal electrode to form a compound, or a metallic compound that segregates on or at the periphery of the internal electrode is allowed to contain during forming internal electrodes in the ceramic in the step for preparing the ceramic green chip, thereby enhancing adhesive property between the internal electrode and the ceramic.
Although the method for manufacturing the ceramic electronic component according to the first and second aspects of the present invention can be applied for manufacturing various laminated ceramic components without any restrictions, it may be applied in the method for manufacturing a ceramic capacitor according to a specified aspect of the present invention. The ceramic green chip to be used in obtaining a laminated ceramic capacitor comprises a plurality of the internal electrodes being laminated via the ceramic layer, and has a structure in which the plural internal electrodes alternately extend along the direction of thickness to a pair of the end faces of the ceramic green chip in opposed relation one another.
The present invention also provides a monolithic ceramic electronic component obtained by the method for manufacturing the monolithic ceramic electronic component according to the present invention, comprising: a ceramic sintered body; at least one layer of internal electrodes disposed within the ceramic sintered body; and external electrodes formed on the outer surfaces of the ceramic sintered body and electrically connected to the internal electrodes, wherein the metal constituting the metallic compound contained in the ceramic forms a solid solution with the internal electrode or reacts with the internal electrode to form a compound in the ceramic sintered body.
The present invention further provides a monolithic ceramic electronic component obtained by the method for manufacturing the monolithic ceramic electronic component according to the present invention, comprising: a ceramic sintered body; at least one layer of internal electrodes disposed within the ceramic sintered body; and external electrodes formed on the outer surfaces of the ceramic sintered body and electrically connected to the internal electrodes, wherein the metallic compound contained in the ceramic sintered body is segregated on the internal electrode or at the periphery of the internal electrode.
Examples of the monolithic ceramic electronic component according to the present invention may include, without being restrictive, a monolithic ceramic electronic component wherein a plurality of the internal electrodes are disposed so as to be laminated along the direction of thickness via the ceramic layer, the internal electrodes being alternately extending along the direction of thickness to end faces of the ceramic green chip in opposed relation one another, and wherein a pair of the external electrodes are formed on the end faces of the ceramic sintered body in opposed relation one another.
Details of the embodiments according to the present invention will be described hereinafter.
First Embodiment
A non-fired ceramic green chip is prepared at first in the method for manufacturing a monolithic ceramic electronic component according to the first embodiment of the present invention. The non-fired ceramic green chip comprises at least one layer of the internal electrodes as well as a metallic compound containing a metal that forms a solid solution with the internal electrode or react with the internal electrode to form a compound during firing.
Electrode materials constituting the internal electrode are not particularly limited, but appropriate metals such as Ag, Pd, Cu and Ni, and an alloy such as a Agxe2x80x94Pd alloy, that are available for a conventional internal electrode material in the monolithic ceramic electronic component may be used. Ceramic materials constituting the ceramic green chip are also not particularly limited, but appropriate ceramics such as dielectric ceramics, magnetic ceramics and piezoelectric ceramics that are available for conventional laminated capacitors and laminated inductors may be used.
Metallic compounds comprising a metal that forms a solid solution with the internal electrode or reacts with the internal electrode to form a compound during firing may be appropriately selected depending on the metallic material constituting the internal electrode. For example, the metallic compound containing a metal that forms a solid solution with the internal electrode includes a compound of Cu, Au or Pd when the internal electrode is formed of Ag, a compound of Ag or Au when the internal electrode is formed of Pd, a compound of Cu or Co when the internal electrode is formed of Ni, and a compound of Ni or Ag when the internal electrode is formed of Cu.
Metallic compounds comprising a metal that forms a compound by reacting with the internal electrode may be also appropriately selected depending on the metallic material constituting the internal electrode. For example, a compound such as PdO may be used when the internal electrode is formed of Ag, a compound such as Bi2O3 may be used when the internal electrode is formed of Pd, compounds such as MgO and Al2O3 may be used when the internal electrode is formed of Ni, and compounds such as NiO and Al2O3 may be used when the internal electrode.
The metallic compound containing a metal that forms a solid solution with the internal electrode, and the metallic compound that forms a compound by reacting with the internal electrode may be used together.
Although the content of the metallic compound that forms a solid solution with the internal electrode, or forms a compound by reacting with the internal electrode in the ceramic, cannot be definitely defined since it differs depending on the kind of the internal electrode material and the metallic compound, the desired electrical characteristics of the monolithic ceramic electronic component may be deteriorated when the content of the metallic compound is too high. Accordingly, the metallic compound is desirably contained in a proportion of about 3% by weight or less in the ceramics after firing.
The method for preparing the non-fired ceramic green chip is not particularly restricted, but it may be prepared according to the method for manufacturing conventional monolithic ceramic electronic components. For example, a ceramic green sheet may be obtained by forming a ceramic slurry into a sheet after preparing the ceramic slurry containing the metallic compound as described above. The ceramic green sheet can be obtained by screen-printing an internal electrode paste on the ceramic green sheet, and laminating a plurality of the ceramic green sheet on which the internal electrode has been printed, followed by laminating plain ceramic green sheets on and under the laminated ceramic green sheets.
The method for forming the internal electrode is not restricted to screen-printing of a conductive paste, but any film-coating method such as vapor-deposition, plating or sputtering may be used.
Alternatively, the non-fired ceramic green chip may be prepared by alternately depositing the ceramic paste and a material constituting the internal electrode on a support, after preparing the ceramic paste containing the metallic compound.
The adhesive property between the ceramic green sheets, or between the ceramic layers, can be enhanced by pressing the green chip along the direction of thickness, prior to firing the green chip.
Baking of the internal electrode and sintering of the ceramic layers are carried out by firing the laminated green chip. The metal constituting the metallic compound may form a solid solution with the internal electrode or may react with the internal electrode to form a compound. As a result, the adhesive property between the internal electrode and the ceramic layer is effectively enhanced by forming a solid solution or by a reaction between them.
After obtaining a ceramic sintered body by the method as described above, external electrodes are formed on the outer surfaces of the ceramic sintered body. The method for forming the external electrode is also not particularly limited, but an appropriate method such as coating and baking of a conductive paste, plating, vapor-deposition or sputtering may be used. The external electrode may be also formed by a combined method of the foregoing methods or may be formed to be laminated metal films.
The metallic material constituting the external electrode is also not particularly limited, but appropriate metallic materials such as Ag, Sn and Ni that are conventionally used for the external electrode of the monolithic ceramic electronic component may be used.
The monolithic ceramic electronic component according to the present invention can be obtained by the procedure as described above.
At least one layer of the internal electrode may be disposed in the ceramic sintered body for use in the monolithic ceramic electronic component according to the present invention or, in other words, the number of lamination of the internal electrode is not restrictive.
The adhesive property between the internal electrode and the ceramic is enhanced, as hitherto described, because the metal constituting the metallic compound contained in the ceramic forms a solid solution with the internal electrode or reacts with the internal electrode to form a compound in the monolithic ceramic electronic component obtained. Accordingly, delamination may be effectively suppressed thus enabling reliability of the monolithic ceramic electronic component to be improved.
Second Embodiment
A metallic compound that segregates on the internal electrode or at the periphery of the internal electrode during firing is used for preparing a non-fired ceramic green chip in the second embodiment of the present invention, instead of the metallic compound that forms a solid solution with the internal electrode or reacts with the internal electrode to form a compound. The other manufacturing steps are the same as used in the first embodiment.
While examples of the metallic compound that segregates on the internal electrode or at the periphery of the internal electrode include CuO, MgO, SiO2 and CaO, the kind of the segregating compounds may be appropriately selected depending on the materials for use in the internal electrode.
The content of the metallic compound that segregates on the internal electrode or at the periphery of the internal electrode is, through it may be different depending on the kind of the metallic compound, desirably about 3% by weight or less. When the content exceeds about 3% by weight, electrical characteristics desirable for the ceramic sintered body may fail to be exhibited.
Segregation on or at the periphery of the internal electrode during firing corresponds not only to segregation on the surface of the internal electrode, but also to segregation in the vicinity of the surface of the internal electrode.
Since the second embodiment of the present invention is similar to the first embodiment of the present invention, except that a metallic compounds that segregates on the internal electrode or at the periphery of the internal electrode is used as described above, the description in the first embodiment will be cited herein and the other descriptions are omitted.
A monolithic ceramic electronic component according to another embodiment of the present invention is obtained by forming external electrodes on the outer surfaces of the ceramic sintered body in the second embodiment. Since the metallic compound contained in the ceramic sintered body segregates on the internal electrode or at the periphery of the internal electrode in the monolithic ceramic electronic component, the adhesive property between the internal electrode and the ceramic layer is enhanced by segregation of the metallic compound. Consequently, delamination is suppressed as in the first embodiment, thereby to effectively improve reliability of the monolithic ceramic electronic component.
The present invention may be generally used for the monolithic ceramic electronic components including, for example, laminated capacitors, laminated inductors, laminated piezoelectric components, laminated thermistors and ceramic-coated substrates.
A laminated capacitor is constructed using a ceramic green chip comprising a dielectric ceramic containing the metallic compound as hitherto described.